Notes:
with the diffusion sock removed (with or without the shield place), the readings are approximately 3 f-stops higher
with the light-blocking shield removed (sock still in place), the readings are approximately 4/10 of an f-stop higher

Wattseconds

Expected Output at 10 feet (ISO100)

Expected Output at 5 feet (ISO100)

Guide Number

A

1320 Ws

f16 +2/10

f32 +2/10

172

B

640 - 660 Ws

f11 +2/10

f22 +2/10

121

C

320 - 330 Ws

f8 +2/10

f16 +2/10

86

D

160 - 165 Ws

f5.6 +2/10

f11 +2/10

61

E

80 - 82.5 Ws

f4 +2/10

f8 +2/10

43

F

40 - 41.25 Ws

f2.8 +2/10

f5.6 +2/10

30

G

20 - 20.625 Ws

f2 +2/10

f4 +2/10

21

H

10 -10.3125 Ws

f1.4 +2/10

f2.8 +2/10

15

I

5 Ws

f1 +2/10

f2 +2/10

11

J

2.5 Ws

n/a

f1.4 +2/10

8

Notes:
with the diffusion sock removed (with the shield still in place), the readings are approximately 4/10 of an f-stop higher
with the light-blocking shield removed (sock still in place), the readings are approximately 1/2 of an f-stop higher
with both the sock and shield removed, the reading are approximately 1 f-stop higher

Wattseconds

Expected Output at 10 feet (ISO100)

Expected Output at 5 feet (ISO100)

Guide Number

A

1320 Ws

f11 +7/10

f22 +7/10

144

B

640 - 660 Ws

f8 +7/10

f16 +7/10

102

C

320 - 330 Ws

f5.6 +7/10

f11 +7/10

72

D

160 - 165 Ws

f4 +7/10

f8 +7/10

51

E

80 - 82.5 Ws

f2.8 +7/10

f5.6 +7/10

36

F

40 - 41.25 Ws

f2 +7/10

f4 +7/10

26

G

20 - 20.625 Ws

f1.4 +7/10

f2.8 +7/10

18

H

10 -10.3125 Ws

n/a

f2 +7/10

13

I

5 Ws

n/a

f1.4 +7/10

9

J

2.5 Ws

n/a

n/a

Notes:
measured at 10 feet, the readings between all three rectangular softboxes were the same +/- 1/10 of an f-stop

This chart provides the expected output for all Paul C. Buff™ standard flash units at both 10 feet and 5 feet in whole f-stop increments. Readings taken at ISO100, see the full notes on all readings at the bottom of the page.

Use the Flash Unit Legend (below) to reference the Wattsecond ratings for each flash unit. For example, if you want to know the expected output of a B800 at half power (-1f) with the 7-inch reflector, first select the 7-inch reflector from the drop down menu. Using the legend, you can see that the B800 at half power is in group D – producing 160-165 Ws. The output chart indicates that the reading for group D is f5.6 +9/10 at 10 feet and f11 +9/10 at 5 feet (GN# 77).

Notes on Expected Output:
These output readings have been measured with a Sekonic L358 flashmeter set to 1/125 second shutter speed at ISO 100, placed 10-feet and 5-feet from the flashtube for direct reflector specs. Readings were taken in a 14-foot x 14-foot room (with an average ceiling height of 14-feet) with both the walls and floor painted grey. Please note that readings may vary when taken in other environments and with other meters, as different brands of flashmeters can vary in their interpretation of correct values.

Notes on Guide Numbers:
The Guide Number (GN) is a standard measurement serving to indicate a flash unit's output by calculating the distance times the f-stop, with respect to the film speed (GN = f/number x flash-to-subject distance). This term is not wholly reliable for comparing flash units because it relates more to the angle of the reflector than to the actual amount of light produced. For example, a flash unit with a given amount of light output will register a much higher guide number (f-stop at 10') if it has a narrow angle reflector (for telephoto lens) than if it has a wide angle reflector. But the actual amount of light is the same in both cases…it just covers more area with the wide angle reflector (at a lower guide number). Studio flash units are designed to be used in many different configurations, with different accessories. The angle of coverage will be different in each case as will be the achieved guide number for a given amount of emitted light.